This invention relates to standards and coatings. More specifically this invention relates to the use of fluorinated polymers as general reflectance standards and coatings.
For many years industries which must measure, test or otherwise use light reflectance have been faced with the problem of having to use materials for general reflectance or reflectance standard purposes (i.e. either white or colored light) which are either unstable to light and thus age poorly or which reflect a low percentage of incident light and thereby fail to meet the degree of quality necessary to effect good reflectance. This problem is especially acute in those industries where these materials must be used either as reflectance standards or as reflective coatings in light integrating spheres used in various measuring and testing devices such as spectrophotometers, colorimeters, and spectrofluorometers. Devices of this nature are well known in the art and are best exemplified by the Pineo Spectrophotometer (U.S. Pat. No. 2,107,836), the Taylor Absolute Reflectance Instrument (Scientific Papers of the Bureau of Standards, Vol 17, pp. 1-6, 1922), the General Electric Spectrophotometer, the IDL "Color Eye," and the Beckman "DU."
Examples of materials currently used for reflectance coatings and standards which give rise to the above problem include pigmented paint, smoked magnesium oxide, magnesium carbonate, and barium sulfate. Pigmented paint, for instance, may be of low reflectance, give rise to light stability problems, and may crack and chip upon aging. Magnesium oxide and magnesium carbonate have been used for many years but their reflectance characteristics and physical properties present problems of light stability and reflectance inefficiency. Barium sulfate, presently the most commonly used white light reflectance standard and sphere coating material, can be made to reflect essentially 100 percent of incident light having a wave length from 2400 to 8000A and thus forms an almost ideal white standard. However, this compound is easily degraded to only about 90 percent of this value after a few days of use. Degradation of this compound is especially rapid when light having wave lengths from 2400 to 4000 A are used, thus seriously affecting the ability to use this compound in devices for measuring, testing or otherwise dealing with ultraviolet light.
From the above discussion it is clearly seen that a long-felt need has existed for a highly reflective material which is also light stable.